Expressions

- Reordered operator table so that longer operators match first, thus
  disambiguating between ! and !=.
- Eliminated Expression::expand_expression.
- Modified Nibbler to know what a DOM reference looks like.
- Removed alpha equivalent operators (lt, le, gt, ge, not, eq, ne) because
  these are common in descriptions (French: le, ne).
- Modified Arguments and Nibbler unit tests.

src/Expression.h

@@ -48,7 +48,6 @@ private:
   void expand_attr ();
   void expand_attmod ();
   void expand_word ();
-  void expand_expression ();
   void expand_tokens ();
   void postfix ();